Principles

The basis of the prototype remains the same - the bioreporter, a GMO bacteria expressing eGFP (Green Fluorescent Protein) is incubated with a water sample, where the fluorescence is detected optically and can be quantified in order to measure the concentration of Arsenic in the water

A vial containing the water sample we want to test is positioned on a socket through which a fluorescent excitation LED (blue 488nm for eGFP) passes.

GFP absorbs this blue light (λ=475 nm) and emits green light (λ=504 nm) which is detected by a photosensor on which the light is concentrated with the help of two lenses that avoid loss of intensity

A long-pass filter allow only the signal eGFP fluorescence to reach the photosensor

Moreover, a red LED was added to measure the transmittance, which can be converted into turbidity. The measurement of turbidity will allow us to normalize our results.

A red LED is placed in-line with the photosensor

We use an arduino to take the measurements, and we have a liquid crystal display (LCD) to read out the numbers.
With these measures, compared against a standard curve of water containing known arsenic concentrations, one can determine the concentration of arsenic in the sample and so know if the water is drinkable or not.

In summary, the most current version consists of:

lasercut chassis
blue LED for eGFP fluorescence excitation at 90 degrees from detector
red LED for transmittance measurements in line with detector
vial holder matching the vial approved by the Swiss authorities
light to frequency detector
a filter to block excitation light
LCD screen read out
based on the arduino

Assembling the Electronics

Each of the PCBs except the LCD screen PCB are fixed onto the lasercut fiber boards using M3 screws.

Soldering and Mounting

Blue LED

Soldering the pieces:

1. the super bright blue surface mount LED (SMD) piece is manually soldered onto the "backside" of the PCB

2. on the "front side" of the PCB, first solder the resistor

3. clip the legs of the resistor from the back

4. solder the other components (the connectors for the Red LED and the light to frequency meter)

5. also the MOSFET??? is soldered in

6. the other MOSFET is soldered into place (redo picture!)

7. to place the ribbon cable connector, first apply solder on one pad on the PCB

8. solder the first foot of the ribbon cable connector, then proceed with the rest

9. all except the resistor for the super bright LED is soldered

10. ready for mounting

Now mounting onto the particle board:

1. M3 screws are placed

2. 2 washers are placed onto the screws before the PCB

3. the SMD Blue LED should face the particle board, and the PCB is bolted in

LCD screen

This LCD screen / arduino shield will connect to the blue LED PCB with a ribbon cable

Soldering the pieces:

1. solder resistor 1 on the logo side

2. place the pins longer pins on the logo side

3. solder from the other side by first anchoring one pin per piece - these pins go into the arduino

4. solder the ribbon cable plug

5. back to the logo side, place the potentiometer on the left, two small buttons on the right and solder into place from the back

6. solder the pins onto the LCD screen

7. LCD screen with view of the pins from the back

8. view of the back with the big button soldered in

9. done soldering

Red LED

1. first mount the red LED - short leg = negative

2. next, the pins, long pins same side as the LED

3. ready to mount on the board

4. mounted, view from the PCB side

5. mounted, view from the LED side

light to frequency meter

LFD 1.JPG

1. place the legs of the light to frequency detector (LFD) in the PCB without bending or soldering

2. use the particle board to align the 'eye' of the LFD

3. solder the LFD and the long pins same side as the LFD

4. back of the soldered PCB aligned with the particle board

5. place a washer to account of the LFD thickness

6. mounted, view from the PCB side

7. mounted, view from the LFD side

Final Assembly

Finally, the Red LED and light to frequency meter will be plugged into the Blue LED board with connectors.

Then the LCD screen is plugged into the Blue LED board with a ribbon cable.

The LCD screen board is ready to be mounted on the arduino.

We are now ready to test it out.

Testing the Electronics

Uploading the arduino code

Reading the measurements

Transmittance and absorbance

Making the Outer Housing

What we have built so far leaves the samples exposed to ambient light. So we need to make outer housing that can mount the LCD screen, house the battery, enclose the rig inside, and have easy access to put the samples in and out while keeping the light and optics dark.